Superconducting cyclotrons are increasingly employed for proton beam radiotherapy treatment (PBRT). The use of superconductivity in a cyclotron design can reduce its mass an order of magnitude over conventional resistive magnet technology, yielding significant reduction in overall cost of the device, the accelerator vault, and its infrastructure, as well as reduced operating costs. At Massachusetts Institute of Technology, initial work was focused on developing a very high field (9 T at the pole face) superconducting synchrocyclotron that resulted in a highly compact device that is about an order of magnitude lighter and much smaller in diameter than a conventional, resistive cyclotron, as described in U.S. Pat. No. 7,656,258 B1. The next step was focused on designing a compact superconducting synchrocyclotron that demonstrates the possibility to further reduce its weight by almost another order of magnitude by eliminating all iron from the device, as described in U.S. Pat. No. 8,975,836 B2. Magnetic field profile in the beam space is achieved through a set of main superconducting split pair coils energized in series with a set of distributed field-shaping superconducting coils to eliminate the magnetic iron poles. External magnetic field shielding is achieved through a set of outer, superconducting ring coils, also connected in series with the other coils to cancel the stray magnetic field. Elimination of all magnetic iron in the flux circuit yields a linear relationship between the operating current and the magnetic field intensity in the beam space. This linear relationship then permits continuous beam energy variation without the use of an energy degrader, thus eliminating secondary radiation during the in-depth beam scanning.